It has long been recognized that the efficiency and fuel economy of an internal combustion engine can be improved by preheating the fuel supplied to the carburetor. Fuel preheating can be accomplished by passing the fuel enroute to the carburetor in heat exchange relationship with engine coolant. Prior art fuel preheaters are shown by way of example in Dunnam U.S. Pat. No. 4,091,782, Rabbiosi U.S. Pat. No. 3,986,486 and DeShaies U.S. Pat. No. 3,253,647, as well as in my U.S. Pat. Nos. 4,476,839 and 4,463,739.
My aforesaid patents disclose a fuel preheater which is adapted for use with an engine coolant system which includes a coolant tube through which coolant can flow and a fuel tube for supplying fuel from a fuel supply to the engine. A portion of the fuel tube forms a coil extending around the exterior of the coolant tube in heat exchange relationship therewith.
One problem with prior art fuel preheaters was that they tended to produce vapor lock under at least some operating conditions. Thus, vapor lock was more likely to occur, for example, on high compression engines or on engines operating in hot desert climates. My U.S. Pat. No. 4,463,739 addressed that problem, but it was found that although the invention disclosed in that patent solved the vapor lock problem, the system was not adequately efficient in very cold climates.